Okay all you 2.5NA haters, have your fun.
Recently my '86 90 ExMod started making a -cha-cha-cha- noise when I start. Matches RPM changes and sounded to me like an exhaust leak. As the engine warms up, the sound goes away.
So I opened the bonnet and put a wrench on the 8 manifold nuts expecting to find one or more loose. All were tight, so gave each a small turn.
Still have the noise. With the bonnet open, it sounds like the -cha-cha-cha- noise is coming from the vacuum pump. (I know, it can be difficult locating noise source in noisy environments.)
Can the vacuum pump make a noise that goes away when it warms up? Does this mean the pump is about to fail? What should I do if anything?