Weird 'flapping' noise ? - Advice please

[stackmonkey]

Can anyone tell me what this is? and if it's symptomatic of a problem?

When I put my foot down, particularly in 2nd and 3rd, as the revs go past 4,000 the car starts to make a loud flapping sound, a bit like a flag in high wind. it seems to come from the exhaust area, but can't be sure. The noise stops when I change up a gear.
My engine pinks a bit sometimes when accelerating, too. Would this be related?

[Big Al.]

Can't say I’ve personally come across the problem.

Just a thought though, have you turned your baseball cap around so the peak faces the back?

[stackmonkey]

I don't wear a baseball cap (particularly around my exhaust area!)

[apprentice]

You've probably inadvertently picked up a Chavy Euro 2004 flag!!

Inspect, remove and retain for World Cup.

[apprentice]

bttt stackmonkey... hopefully it won't attract yet another wisearse!!

[stackmonkey]

Umm, anyone got any useful answers to my original question, please?

[bobs4c]

Could be exhaust manifold gasket, but this would show itself at lower revs as well.

[ian8542]

Sounds like pre-ignition. Check the ignition timing is correct.
If it still persists try Shell Optimax or octane booster.

[stackmonkey]

Well it's now booked into John Noble Motorsport in a couple of weeks.

it does have a small seal leak in the exhaust (picked on the pre-purchase inspection) so I'll get that sorted, but it's already running on Optimax.

Hopefully it'll come back running a bit sweeter and smoother. I'l let you all know how it goes.

[spid]

The vacuum advance on the side of the distributor came loose on mine, caused it to pink and make funny noises. Reasembled with locktite now