Mellotronists

<< A couple of investigative shockwave impulses (also referred to as 
"knocks") >>

ah, "percussion maintenance". aka "borrowing the drummer's screwdriver".  the 
heads are supposed to be earthed (grounded) to the pre-amp and not to any 
part of the frame; this is because there're 35 of them and a shit-load of 
gain required for succesful operation. each note adds another 3dB, more or 
less... so any earth currents running around the chassis would be amplified. 
there's something martin or someone else will add about dc coupling and 
gaussing up the heads, which I forget at the moment. I had a corroded 
belling-lee connector going into my pre-amp box (ouch) which I replaced with 
a hard-cable before i knew about this issue, and never had any problems. 
while the corroded connector and old cable was there, I'd get interesting 
crackles (as on "rosemary's baby" on our first album) and occasional 
microphony. JB or martin replaced my cable with a new belling-lee but I think 
they left my extra-thick earth cable in- maybe the pre-amp is decoupled now, 
I'll have to look.

d/m400nr1098