My 2005 GMC Envoy is running poor. It gives off a horrible fuel smell from the exhaust - especially when idling. It recently has started making a rattling sound under the hood - but it is not constant, just happens sporadically. Most recently the reduced engine power light came on and now I can not go more than 40 mph without my RPMs shooting up to 3000+. Now when idling it makes a slow constant tick nose much like a clock. My mechanic can't seem to find the solution. Any suggestions?

SOURCE: Engine Making Noise when accelerating

Could be carbon build-up on the pistons, causing erratic flame travel in the combustion chamber... 'pinging'...... Decarbon the engine and use a high grade fuel for a few tanks.... also an octane booster can help

SOURCE: 04 Endeavor rattling noise

I had the same problem! I crawled underneath the car and discovered that a heat shield on the exhaust header pipe was corroded and rattling against the exhaust pipe. (Before the muffler)
I removed the portion and clamps and solved the problem. Give it a try.

SOURCE: 2001 Buick Regal, 3.8L, 98,000

This happened to my 2001 Regal... There is a factory recall on the Catalytic Converter going bad. I had mine replaced with the recall and haven't had a problem since

SOURCE: fuel pressure regulator makes hissing sound

your fuel pump should cycle on until the proper fuel pressure is achieved then it should shut off

SOURCE: 2000 Lincoln Navigator Stalling at low RPMS sporadically

Idle Air Control (IAC) motor is sticking.You can try taking it off and cleaning it but most likely will have to replace it.