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My 1997 BMW 318is started making a whirring noise that varies with engine speed, and an electrical burning smell after driving, and the battery goes flat very quickly.

I measured the current draw with everything off and no key in, and it is constantly around 3.5 Amps.

I tried removing every fuse and relay from under the bonnet, then every fuse, module and relay I could find inside the car. Nothing stopped the current draw.

I then removed the power lead to the starter motor/alternator/unloader relay and the current draw stopped. (There is not good access to the starter itself so I wasn't able to just disconnect the starter on its own.)

My theory is the starter solenoid is always energised so is drawing the current, and that could cause the whirring noise as the starter might be permanently spinning with the engine. The burning smell could be because the starter is not designed to spin at driving engine speeds.

Is this likely? What would cause the solenoid to be permanently energised even with no key in the car? Could it be the starter motor itself?

Someone suggested the unloader relay but I have no idea where it is... I may have already disconnected it. Could it be the cause?

Would it be safe to drive the car 5 minutes to a garage if I keep the engine speeds as low as possible?

Update: I was able to disconnect the big red wire on the back of the alternator only, and the current draw stopped. Does this mean the alternator is the cause?

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First of all, eliminate everything else of the final things you pulled prior to assuming it's the solenoid on the starter, but I think you are onto it with the starter. You would have all of these symptoms with a starter motor which is engaged all the time. I'd suggest you are going to end up replacing the starter anyway ... the drive to the mechanic if only a few miles away is not going to cause it any more damage than it has already experienced. At this point, if you are going to utilize the mechanic, I'd just drive it there directly and put it into their hands.

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The problem turned out to be the alternator.

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