It seems to be a telling fact that many reports of ghosts and hauntings start when a previously 'quiet' location or building undergoes alteration of some kind; often starting almost as soon as the first bit of work is barely complete.
The question surely must be - Why!?
It certainly appears that disturbing what is known to them is something that some ghosts and spirits do not like or, at the very least, do not appreciate. Much like life really, how many living people go on marches and demonstrations when something that they do not want disturbed, built, renovated, demolished or 'despoiled' is in the offing ... it seems to happen somewhere every week. The main difference being that the living know in advance and take action, ghosts and spirits only get to know when it's actually happening.
There is probably a good article waiting to be written concerning the apparent contradiction in that statement with the accepted belief that the occupants of the spirit world are ahead of us (as it were) on being able to foresee future events. However - it is no contradiction if thought about this way. Many ghosts haunt as they are not in that spirit world - they are bound to the location of their haunting for a variety of reasons. So ... they see no further into the physical world or into the future than the surroundings that they are bound within. They can only react after or during the event - when things change within their horizons.
It might be that spirits do not like change and different spirits dislike it for different reasons.
Although far from a comprehensive list of the various types of ghostly or paranormal phenomena, the ones highlighted, below, will perhaps give an understanding as to why alterations to their abode, brings some ghosts out into the 'open'.
There are those ghosts that are totally unaware of what is currently surrounding them and go through their routine without deviation. The thinking behind hauntings of this kind is that they are not actual spirits or ghosts but an event has been 'recorded' within the location's structure - and so we see a play-back of an incident, or hear the associated noises. How can 'recordings' be affected by alterations if there is no spirit soul present to notice things have changed? If the recording is recorded within a structure, then a change to that structure might trigger the replays. Or the change in the structure and in the way it retains the recording may alter the replay effect so that it becomes visible or audible - when before it happened unseen or unheard.
Spirits tied to a location through things left undone - or trying to gain forgiveness for deeds done in life - or trying to remedy some mistake ... what of them and alterations to their world? Many such questing spirits do not need alterations to start to haunt, it just takes someone that they believe could help them in their quest. But some appear to be 'dormant' until their surroundings alter. It could be that these are spirits who have quested but did so locked in their own time and so ... outside of our awareness of them. The alterations create a breach in their 'time surroundings' through which they can enter our current world.
This can bring forward two kinds of such ghost. Those that are still not aware of us but who do not repeat the same actions, still moving in the time of their own perception - but now visible or audible to us. Or, those that can move between the two times of their existence and who are aware of that situation. These seem to eventually come more and more into our world but still maintain their old quest.
Similar to a ghost or spirit held in a location because of an unfulfilled need, are those that are very aware of where they are but have 'gone into hiding' or are terrified of 'moving on'. Many hauntings stem from souls that have a stained life history and refuse to budge from our dimension through fear of what their fate is in the next. It is sometimes the case that their need to continue their misdeeds will overcome their need to stay hidden and if other opportunities present themselves, such as a potential 'victim' coming along, then they will betray their presence. Others though will not dare give themselves away - until something happens to make them feel unsafe.
This is frequently some form of renovation or alteration to their 'hiding place'. It 'opens up' the fabric of their protective little world and they feel exposed - discovery of any kind is the last thing that ghosts and spirits like this want so they 'come out' with the intention of 'hiding' elsewhere in the newly created situation in which they find themselves.
A usual form of manifestation, in this type of case, is that they can attach - as an entity - to someone in the location and/or can present as a misunderstood soul to gain support and sympathy ... trying to gain the protection of the living. All sweetness and light but letting all and sundry know that they are so, so sad. Until, that is, they feel that they are threatened because the living want them out or their 'protectors' do something - even unwittingly - that might loosen the grip that the spirit has, through them, on this dimension ... or if the spirit's true nature is discovered. To this kind of soul, alterations of any kind to its circumstances are dangerous to them, so sweetness can become very malevolent and threatening when this happens. Intimidation becomes its last form of protection.
Then come ghosts that are bound to a place that they love and where they keep themselves to themselves, happy in their own world and never bothering the living. Alterations happen and the ghost reacts by becoming noticed and noticeably not happy with the changed situation. The meek and unassuming spirit that was content in the status quo becomes an irate handful for the living to live with. Surprisingly, this kind of outraged (once demure) presence can be the worst of spirits to both live with and to placate ... or to try to move on. It boils down to revenge and taking it out on the living world - often with a tenacity of haunting that is remarkable.
Finally and not to be overlooked, are the more supernatural or spiritual outbreaks of activity when building or alterations are carried out to a location. The prime example of this is where buildings are erected - or an area is somehow deliberately disturbed - and the ground in question is sacred to the dead. In this situation, we might be upping the stakes somewhat from disturbed ghosts to the disturbance going far deeper into the spiritual fabric and a whole new realm of possible angry entities and existences could be brought into focus. This is mentioned only in passing as it would require an article in its own right to even summarise the possiblities.
To those who find that after a bit of renovating, altering or even simply decorating - a ghost seems to just show up ... it might have been there for years and has been content not to be noticed - until it got disturbed.