How to tell if it's a front diff, axle, or transfer case? Car at times slows down and pulls to the right at times

[killerbeez]

Ok guys I've heard some noise coming from what I thought was the front diff on my 330xi, i did notice it leaking and topped it off recently but it may have ran low before I caught it. I hear it in park even and it seems if I rev up the engine and let off it will kind of stop. but it's not an engine noise.
Today now, I noticed I was going and the car bogged way way down and started to pull to the right, then after a few seconds it "caught" and started going again for a bit, only to repeat the slowdown.
So, I'm going to take a look at it but these days of new born fatherhood my time to investigate things is extremely limited so I'm trying to get the scoop before i start checking things out. Can anyone give me advice on how to narrow it down to an axle, diff, transfer case, etc.?
Thanks much in advance!

Edited December 2, 2023 by killerbeez

[momo]

Your drivetrain cannot make noises if in park - it's not moving and no gear is engaged! If the car is making noises when standing still it has to be engine related.

You may be better off taking it to a mechanic who can diagnose it for you.