funny noise from engine

[myoldjalopy]

I have a mysterious new noise! It is connected to the engine but strangely doesn't rise in pitch as the engine runs faster, only slightly louder, but is most audible around 40mph (higher speeds the engine noise itself drowns it out) and disappears at tickover. Very hard noise to describe - not banging, rattling, clanking etc. More like a cross between a hissing and a buzzing and not too loud. Annoyingly, it is hard to hear with the bonnet open, even when revving the engine, but an open window when driving makes it easier to hear. Can't be too serious as I have put up with it for a few hundred miles now and no problems.
Any thoughts, anyone?

[bmcecosse]

Exhaust leak?? Or - take the fan belt off and do a very short drive - does the noise go away then?

[moggiethouable]

Only when moving?
New roof rack,wing mirror or badge rack?

[lambrettalad]

exhaust manifold leak?

[myoldjalopy]

Thanks for your replies. No it is not an exhaust leak. When I said a cross between buzzing and hissing, it is nearer to buzzing - or even a very light scraping. Very difficult noise to describe. I will try the take off fanbelt and see what happens (apart from overheat!) Wondering if waterpump, dynamo or distributer??

[JOWETTJAVELIN]

Sounds perfectly normal for an old crock to me.

[bmcecosse]

Run without fan belt will eliminate water pump and dynamo -and bottom drive pulley! Check that - because they are known to crack and break up with age......