Mystery noise

[z_rawi]

I have a UK 1994 MX-3 V6 1.8i.<P>I've got a mystery noise from my car engine bay. I can only hear it from the cabin with the windows closed. It sounds like "diga, diga, diga, ..." at a frequency of about 2-3Hz. It comes on at ~1500rpm and is of constant frequency regardless of engine revs above this.<P>So I guess it's not the engine but something else like an electrically operated piece of kit or a solenoid?<P>Other problems which might or might not be related are noise from my exhaust at the passenger footwell under heavy acceleration(loose heat shield?) and strange, intermitent, slight losses of power whilst driving at speed (faulty sensor in distributor?).<P>Any suggestions as to the likely cause of the noise, etc gratefully appreciated!

[z_rawi]

Problem solved. An engineer friend diagnosed the problem(s) which helped the garage to find them.<P>I had a faulty solenoid valve on the engine bulkhead, that's a lot better than a faulty engine!<P>Flat spots on acceleration turned out to be a split vacuum hose.