I've never run into this problem before. I just got an old Peavey Backstage 110 and I can hear the impact of anything tapping or hitting my guitar cable. Its pretty extreme to the point that I can't really move while playing because the movements of the cable sound through the amp.

They're not low quality cables either. This only happens on this amp.

Does anyone have any idea what this could be? It'll be a cool amp if I can get this fixed but its kind of unusable if I always get this nasty cable noise. Thanks for any feedback.
Check your amps input jack, if its loose, that could be the problem, you might also wanna check your guitars input jack.
Other than that I can't really think of anything else, it might just be that the amp hasn't been looked after well enough before you bought it.
Hope this helps :P
Cool. I know its not the guitar but I'll definitely check out the amp input jack. Truthfully, the amp isn't in really fantastic condition but I just wanted to know what this could be because I've never run into it before and I don't really even have any of my own ideas about what it could be. Thanks though, I'll look at it.