Jumpy/no acceleration & loud hum from eng bay
E39 530D 2002 Manual (UK). I've had the car for about 5 years and apart from having to replace the FSU last year it's been as good as gold! It has done about 90K miles - 60K of them with me since I bought it in 2006 - and has been serviced as dictated by the lights!
Before I give in and take my car to the garage I thought I'd ask the experts here! Please bear with my descriptions!
I've got two problems which both seem to start around the same time so may be related.
1) Jumpy/no acceleration whilst already moving with accelerator flat down
I first had the problem on the motorway. I was doing about 70 mph and went to accelerate, but there was no response. I tried a few times and had the same problem, and then after a few minutes it would try to accelerate but was very jumpy. This has happened a few more times, including at lower speed. I've tried to work out a pattern, and it seems to happen more when the the engine is at normal temp, and happens in all gears.
I thought initially it might be DSC related as the no response felt similar to when that kicks in, but the dashboard light doesn't flash like it normally does when it kicks in. The problem still happens with DSC disabled. The dashboard light did come on and stay on whilst driving a couple of months ago, but then stayed off so I didn't look into it more.
2) Loud hum coming from behind passenger dash, with ignition in On position for 60 seconds
Everytime I turn the key to On, but before starting, there is a loud hum coming from behind the passenger dash. I think it's coming from the engine bay but its hard to pointpoint the noise. The noise happens for exactly 60 seconds and then stops (which will hopefully help diagnose the problem). The hum is fairly constant with the odd fluctuation, and is sometimes v loud but can be a bit quieter. The noise also happens intermitently when I'm driving.
Any help/pointers/suggestions would be hugely appreciated. Many thanks in advance.