What is the loud hissing noise when accelerating

Hi, Please check you engine oil as a first start. A loud noise could indicate engine failure or engine auxiliary components failure. You can know if the sound is tapping or knocking or if the sound is rubbing or grinding sound due to rotation. At time you may have a drive train fault

a vacume leak from one of your hoses

possibly the diverter valve. Pretty common problem. There was a TSB concerning those.

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The the exhaust system must be clogged, how about the muffler?

We do not hand out medical advice here. Try WEBMD.com

If it seems to have a loss of power you may have a clogged exhaust, (muffler) system, again if you have a loss of power or it runs ruff check for a vacuum leak.

SOUND LIKE LOW COMPRESSION.EXCESSIVE CARBON INSIDE ENGINE CAUSE ENGINE TO DIESELING KEEP RUNNING MAKE A RATTLING NOISE WHEN YOU TURN OFF IGNITION.

sounds like a plugged up catalytic converter

exhaust leak,or blocked,squashed exhaust,may be turbo pipes leaking or loose,have to get the obvious looked at first,then get mechanic who knows to look at it,dont cut corners,gets expensive

Check for exhaust leaks. Esp Leaks toward the front of the car. Hold your hand over the tail pipe using a rag and see where the loud hissing noise comes from. Repair the leaks and I bet the backfiring goes away

Good Luck