The thing is that the B757 has a Mach/Speed trim system, the B767, at least according to any books I have as an instructor on the twin sisters doesn´t. At least it definitely does not have a MACH/SPD TRIM EICAS Warning, which comes on every now and then on the B757.
A quick fix is to disconnect the autopilot and toggle the Stablizere trim thumb switches or the ALTN STAB TRIM SWITCH/HANDLE and it usually cures it instantly.
No further need to bother maintenance.
Cheers.