240 DL sedan 1989 150K miles

I have realized that my newly installed fuel pre-pump is loud.

Recently I replaced the sender/hose/pre-pump/sock assembly. All went well.
All this was replaced with new parts I bought from fcpgroton.com (I think VDO).

I have noticed that the pre-pump is relatively loud. By that I mean that I can actually hear the buzz from sitting in the driver's seat with the car running, doors closed, radio off. It can also be similarly heard when openeing the trunk (sedan). I did cover the cap in the trunk and siliconed to seal.

BTW the buzz is not the main pump. If I pull the pre-pump fuse it goes away, car still runs (as normal). The main pump is original I think and dead quiet.

So how loud is this pre-pump supposed to be?
Are there maybe quality issues with the replacement?

Another question that just came to mind: I assumed that the polarity of the wire connection (ground and +12V) to the pump was fixed (DC pump). The wires actually only went one way since they had a plastic sleeve on them... The replacement pump looked identical to the original one in every respect. Was I correct to assume that there was no chance of mixing the polarity (+ to - and - to +) when connecting it? makes sense....

Any other ideas why this is loud, or maybe should it be? It is absolutely not to any annoying level, just wondering if hearing it from inside the car was normal. BTW it has maintained the same volume from the moment I put it in 1K miles ago. All appears to work great.

Thanks in advance,
Greg Mustang