not so sure about the fan clutch as some suggested
i have a 4.4i X5 and it makes similar sound
also have 3.0i X3 with no viscous fan and it makes a similar sound .
the sound of yours is very loud .
ours get a bit louder when turning the steering , even just a slight input causes an increase in sound .

Ok, I assumed the tensioner and idler for the alternator belt was replaced vs the 2 tensioners. Did you change the idler pulley yet? (bolts on at the bottom of the alternator housing) It still sounds like a pulley noise, so if they changed the 2 pulleys on the alt belt tensioner setup that still leaves 2 more pulleys total with the tensioner for the other belt and the deflector pulley on the alt belt. (4 pulleys in question total)

Also, does the noise change at all with ac operation? (just to isolate the ac compressor clutch, not common on BMWs)

RealOEM.com BMW E53 X5 4.6is Belt Drive Water Pump/Alternator

RealOEM.com BMW E53 X5 4.6is Belt Drive Climate Compressor

With diesel engine a cracked exhaust manifold is quite common and known problem, but I'm not sure if V8-models has the same issue. Problem appears as a whistling sound which is dependent on engine revs. With diesel you can look if engine is black and dirty around exhaust manifold (due leaking) but I would assume petrol engines run a bit cleaner. You could take a look though...

Yep, had that same exact sound on my 4.6iS @ 65K miles...turned out to be the torque converter. If it is, the longer you continue to drive, the more damage it will cause to your trany. In my case, instead of having it rebuilt, i went with the upgraded OEM, a bit more expensive but i swear it pulls harder than the previous or a rebuilt version.

Funny enough, my buddies 95 750iL that is sitting in my garage makes a similar type of noise that i've been trying to remedy myself also. I really need to find a way to record it, but i'm afraid it's not as distinct as your noise is, and it only happens from a dead stop for his car. I thought it was a power steering pump issue at first since it sounded like Ford's sitting at idle and turning the wheel. I've removed each belt, one at a time, but nothing changed. It's definately drive related since I can't get the sound to happen while sitting in park or neutral. I did a fluid/filter change w/ Castrol Multi Import, but that didn't change anything either.

Hey Weasel, do you know if a 95 750 TC and a 98 740 TC are compatible? I could look on RealOEM, but maybe you'll know right away. Unfortunately I know of 1 junkyard in my area that has an E32 740/750 (can't rememeber), otherwise I'd have to buy something online, have it shipped and hope to god that was the culprit. Also, I've heard of people swapping 740i Sport TC's into iL's for it's higher stall speed...is the same thing possible in the 750 if I'm forced to buy something online?

How was it upgraded? Like I wrote above about 7's, so did you use one from a 4.8 instead?

Not sure which tensioners where replaced as I no diagram shows up in the second link. Here is a pic of the tensioners I had replaced.

http://i255.photobucket.com/albums/h...c/P1000847.jpg

I thinking it is the torque converter as I have a fluid leak that appears to be coming from the bell housing where the tranny and engine meet. Also after shooting the video there seems to be an intermediate rattle sound of sort coming from that area.

I am also considering taking the X to the stealer. I trust my Indy as he takes care of my cars and my friends cars. Just losing confidence in his ability to diagnose the issue.

More info please on what you did. What upgraded OEM?

The 95 750il has the A5S560Z tranny as the 98 740i has the A5S440Z tranny, but the torque converters are the same... so if the TC swap works good from 740i sport to 740il, it should work the same for the 95 750il which has the same converter as the 98 740il. (I was curious and did the realoem work to confirm :D)

The fluid leak you see is most likely from the oil pump (trany?)...mine wasn't leaking but i recall discussing an oil pump to the trany with the tech that performed the diagnosis and repair so decided to replace anyway.

I had just replaced valley pan, alternator, pulley's, drive belts, cooling & heating system components so i was already in repair mode when the TC noise appeared. I had a diagnosis performed to confirm that it was the torque converter. The SA mentioned that i could go with a rebuilt TC but there was some sort of upgrade with the 4.6iS OEM TC converter...so i purchased a new one from dealer. He also mentioned that the more i drove the X the more damage to the trany so i addressed the matter immediately. Fortunately, i've become friends with the tech that did my repairs so labor cost was at a friendly discount :D

Are you experiencing any drive-ability issues, trany-wise?

I am guessing the TC had a higher stall than stock. Any chance you could get the part number of this TC?