Thing,
I'm only a humble PPL, so if any ATPL wants to correct my following reply - feel free.
The noise from thrust reversers varies between aircraft types, when heard in the cabin - when used fully. However, they are not always used fully. Most pilots use them to some extent - to save the brakes - but if the runway is long and they want to exit at a taxiway further away from the threshold they may be used only at idle. In that case, chances are you wouldn't hear them.
The noisiest is when they want to quick exit from an early taxiway or the runway is very short (try Gibralter!). Then they may use full reverse thrust - very noisy, lots of vibration and noticable slowing down.
Use of reverse thrust may be noisy, but it is never dangerous (unless asymetric, in which case a marked yaw may develop
)
If you want an interesting one, try flying in a turboprop that has reverse thrust on the variable pitch propellors!
Note, some types don't have reverse thrust at all - e.g. Embraer 145, BAE 146.
Hope this helps.
HH