Musicians Roadhouse

I got this old Premier unit a few weeks back. Sounds pretty nice except it sounds like the springs are slightly vibrating as it has like a ticking noise. All the Electrolytic smoothing(filter) caps have been replaced, the AC Mains cable swapped to an earthed (grounded) cable and some of the signal path caps replaced (had those horrible ceramic disc caps in it). But getting this odd sound like the springs are making noise..
Any ideas?
Cheers/Thanks!
BTW, the tank is an old Accutronics one that is the same tank # as Fender used and the valves are a 6EU7 & a 6AK6.