Moog Delay troubles

[Connor]

I bought a Moog super delay on ebay, (number 78/250). the seller said everything with it was fine. but there is a pretty loud hissing / white noise thing going on on the medium delay settings. it sounds like the background noise if you have a high gain pedal going on single coils. does anyone here have a moog delay? either the Z or the SD?
im trying to figure out if this is normal or it needs to be repaired, in which case im going to try to get the seller to do a partial refund to cover the repair cost