The biggest problem with pretty much every rehearsal room I've been in is volume.
You have a room roughly the same size as a single garage and you fill it with stacks by Marshall and Ashdown, plus a PA that could handle the main stage at Glastonbury, and then the band plays at gig volume.
Well gig volume only works at a gig, in a decent-sized room with carpets and furniture and stuff, and above all with dozens (perhaps hundreds) of bodies absorbing the sound.
I've never understood why so many bands are so stupid about this. The only thing that gig volume is good for at a rehearsal is hiding the mistakes ... so why bother rehearsing?
Grumpyguts, try insisting (just once) that the whole band turns down to a sensible level. Turn the singer down on the PA to the point where he's at home stereo level, you take the bass down to match, force the guitarist(s) to follow suit, and then the drummer has no choice.
I believe that you'll be very pleasantly surprised at the result. And your ears won't be ringing the next morning.