Bigguy2017

Perfection... I had gigged one of these '79 - '82. Great punchy tone.

Replace the jack socket - with a genuine Switchcraft (or a Pure-Tone) mono socket Output Jacks – Northwest Guitars Pure Tone Multi-Contact 1/4" Output Jack – Armstrong Music Good for another twenty years... Also, check the existing jack with another cable? It could be a duff jack plug.

Yes, certainly looks like some kind of Music Drive bass - the hooked 'Ric' horns are on the guitars too. Headstock, tuners + truss rod cover are the same. Music Drive (MD) Bass Guitar MCB 6200-f | #463741760 (worthpoint.com) Same PuP and knob layout here MD Music Drive Rare Mahogany Body Natural Bass Guitar - Made in Korea Circa 2000 | Reverb UK Music Drive (MD) guitars and basses were made in Korea by Sumer Musical Instruments Company Limited, from around 2000 Also... https://reverb.com/uk/item/77946719-metal-driver-md-bass-by-sumer-silver-burst-1999-samick-korea They've got a Custom Shop now ... ? ::: MD Guitar ::: (mdcustomshop.com) Your one looks like an MDB-610 https://mdcustomshop.com/kr/product/view.php?id=35&cate=19

An NTC Thermistor in the supply line will do that

I go the other way (ooh vicar) and select a co-ordinated but contrasting coloured strap - this way I get to show off the guitar AND the strap 😉

This suggests the power amp section is AOK and the problem is in the preamp. First stick a jack in/out in all the input and FX send return jack sockets - give them a squirt of contact cleaner. If the opamps are socketed, give them a good push into the sockets. Make certain you have a good working guitar cable... 😉 As usual, look for any bulged or leaky electrolytic caps... Unplug/replug all the internal connectors inc HD3 (preamp / poweramp connections) Also try unplugging the Reverb at HD1 and HD2. If the opamps are socketed, give them a good push into the sockets. Looking at the schematic it appears the preamp supply is Zenered down to +-15 VDC from the +-28 VDC power amp supply. I'd have a good look at the +-15 VDC rails and their smoothing caps C36 C37 C300. Put a 'scope on the +-28 VDC and +-15 VDC rails and look for hum. Obvs, if you have a 'scope (!) you look at the FX send and trace the signal back to the input Take it to a repairman.... 😉 laney_hcm65r_sch.pdf

What sort of noise? Hum, hiss or crackles?

Looks like a film capacitor ? Can't see the part numbers. There are a couple of pages in the manual showing this PCB with the 1K5 15W resistor, cap and fuse. Peavey-T-Max-Bass-Schematics.pdf

100R and 0.1uF is pretty standard

Sounds like a nut/break angle issue. How many turns on the tuner post is the A string? Making the max number of turns (three to four) will force the string to the bottom of the tuner post and may be enough to fix things... if not the nut slot may need some work.

Leaky DC blocking caps on the outputs?

No, it's not right. They should be tapered - should be readily apparent, 'specially on a 1 degree shim. See pics here StewMac Neck Shims for Bass - StewMac

Does the push / pull switch disconnect the power to the preamp or just switch it in / out of circuit? Asking as the most likely reason for battery drain is continuous power to the preamp.