MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Weird droning sound at speed

I have a weird droning sound at speed in my BGT V8, loud enough for me to want to cure it. It appears to need some vehicle speed to initiate it, perhaps over 50 mph, but it is not related to engine speed, i.e. once commenced the tone doesn't alter if you change engine speed or vehicle speed. When I slow sufficiently it then stops. It can also be a bit intermittent.

I had though it sounded a bit like a dry bearing in an electrical motor, perhaps one of the cooling fan motors or the heating blower motor. I usually run with the blower on. When I get the sound I've tried turning the blower off, some times this makes a difference, some times it does not. I think it might be possible for the blower to keep spinning with the ram air going through it from the vehicle speed.

My next step is to mechanical hold the motors from turning (whilst ensuring there is also no electrical power being supplied) and then going for a test run to see if this illuminates the issue. However before that I thought to ask whether anyone has experienced some thing similar.

Thanks James,
James Eastwood

Sounds like the wife ...

Both the heater and cooling fans will rotate at a far higher speed when powered than with just the ram effect, and that's if the heater fan rotates at all with ram. Can't really see it being those, as they would change with road speed. Does this happen from cold? Or only when the engine is up to temperature? If cold that again tends to eliminate the cooling fans. At what speed does it stop happening when slowing down? Anything electrically powered would tend to be constant irrespective of vehicle speed. Does it change with different gears at the same speed? OD in or out?
PaulH Solihull

Wheel bearing?
B Anderson

Universal joints?
Dan Robinson

This sounds more like a differential problem
Iain MacKintosh

Paul - indeed, funny, in fact I had my mother-in-law in the car last time I heard the noise! I'll see if I can define the problem a bit better, thanks.

B.Anderson, Dan, Ian - your suggestions sound worrying. I should at least check the dif oil though as that's on my list anyway. My perception is the noise is coming from under the bonnet or the front end of the car. There is no perceptible vibration either with the noise.
James Eastwood

James - I had a strange noise from the front end, see previous thread on this ('strange noise from my MGB'): http://www2.mgcars.org.uk/cgi-bin/gen5?runprog=mgbbs&access=&mode=archiveth&subject=71&subjectar=71&thread=2012050516462817625

The problem is still unresolved and I'm now getting it with both my MGs. One theory that has been suggested recently is that there is nothing amiss with the cars, but it could be a side effect from tinnitus. I have suffered from a mild form of this for about 15 years but it is gradually worsening. The combined effect of the constant high-pitched whistle I always hear, plus the engine noise, results in a lower 'beat' frequency, which stops as soon as I turn off the engine.
Brian Shaw

Doesn't sound like UJ, diff or wheel bearings if it only starts at 50, doesn't change with road speed, then stops suddenly below a certain speed, and sometimes doesn't do it at all.

Does it vary according to whether the roads are wet or dry? I do remember many years ago having mechanical noise transmitted into the cabin more when it was wet than dry.
PaulH Solihull

Could be an exhaust resonance. Once it starts it stays till the gas speed drops again.
Allan Reeling

It's been quite cold in the UK so I haven'tbeen out in the car. But I had a trawl through the internet and found this article on the 'MG Experince' Forum;

http://www.mgexperience.net/phorum/read.php?1,1140792,page=1

It describes a howling sound, caused by fan motor bearings. So I followed the advice, which is to remove the fan motor drip some oil into the fan blade end bearing, and to drill a small hole in the motor cover through which to squirt some oil into the other bearing. This I've accomplished and will report back when I've driven it.

James
James Eastwood

There is a small probablity it is a bearing but there is an easy check..I had a bearing that only made a noise above 30. It started about 3 months after someone bumped into me in an ice storm. Whenever I took an exit ramp off the motorway at speed the noise would decrease drastically as the weight would come off of the bearing on that side. If it was exhaust it would be easy to coast in neutral at same speed and see if it drops off.
jjralston

It sounds like an airflow noise - air leaving the engine bay - through a gap in the inner wing or past a distorted mud shield or any gap that would funnel the air into a vaguely musical note. There have been some reports of something like this from owners of RV8s.
Roger W

This thread was discussed between 06/03/2013 and 13/03/2013

MG MGB Technical index

This thread is from the archives. Join the live MG MGB Technical BBS now