You have an "offset" going onto the track. The whistle and bell are normally controlled by a rectifier block that uses a series of diodes to offset the peaks and valleys of the sine wave by about 1.5 volts. A positive offset blows the horn/whistle; a negative offset rings the bell. I've seen this with some earlier MTH locomotives on the club layout. A pre-war transformer shouldn't present a problem as those were variable AC, so there is likely some DC leaking into the track from somewhere. I don't recall if the V-150 has a whistle controller, but if it does, you may have a leaking whistle rectifier.
Do you have any accessories tied into the track? Is the transformer shared by anything else like a TIU, or common-grounded to track powered by another transformer? An electronic transformer like a CW80 generates a chopped sine wave and that noise could definitely leak into the system. You may be able to clean that up with a 100uF 35V non-polarized electrolytic capacitor across the A-U terminals. I've attached a Proto-1 reset chart and the QS2Plus manual for how to program the resets. The easiest way is to find a friend with an MTH Z4000 which can enter the codes directly.
