losing power in fifth gear

Sounds like the element inside the catalytic conveter is loose and moving around. This would explain the noise as well as loss of power if its plugging the cat when it moves. I'd get it checked out right away, or you could have a fire(unfortunately as Jonnie Santos can attest to).

Did you get a cheap replacement for the cat when you replaced it?

...mine was loosing power as well and I just thought it was something minor - fire never entered my mind. I assumed the computer would shut the car down if there is risk to the user or something was majorly wrong with the car. Was the Service Engine Soon (SES) light coming on too? To do over again, I would have shut mine off and had it towed to the dealer. It's not worth the risk to people and property over. My 2 cents...

no, I put a new catalytic converter on my car last month. thank you for answering me.your answer was helpful!

...with that ruled off, and assuming the fuel and ignition systems are fine, what about rings and valves? Anyone do a compression test? (I'm just reaching here, I am not a tech, just an enthusiast)

Exactly why I think your catalytic converter is the problem. When a new problem arises, the first place to look is usually the last thing that was messed with. In this case, it was the cat.

It also makes sense; the rattling at idle is the broken up element in the cat, and the loss of power is that broken up element plugging the exhaust system. Get it looked at quick!!

You're really really reaching Jonnie........

I'm about 98% certain the cat is his problem.....

The one he replaced it with was probably a $100 cheapie weld on job and its probably broken already.....

...lets hope he finds out soon. I don't remember if he said the SES light was on either.

With the cat the SES wouldn't necessarily have to be on. As a matter of fact I would tend to guess that a lot of the time one wouldn't even get a code.