My 2002 nissan altima makes a noise coming under the car when i slow down after going 50 mph,whats going on

Does the noise occur when the ac is turned off ?

Needs to be lifted up and have a look ,could be just the heat shield is loose but without a look??

I've just bought a K13 Nissan Micra and it doesn't sound quite right. The noise I hear also seems to be coming from the back but it sounds like when you chop down a gear in a manual going down a hill and the engine revvs, well this is the noise I get in the automatic speeding up and slowing down, even just cruising at a steady speed. Any ideas people? Apart from this noise I love this car.

You have a CVT in the 2009 Altima so there are no true gears. Any noise you hear could be the belt breaking down or the transmission going belly up. Have you had the fluid changed? If not, I suggest you go to a repair shop and get it done. Nissan CVT are notorious at breaking down and typical cost about 4K USD to repair.

Semper Fi,
Z

Just take it into the exhaust people and they will rehang it with new surports plus the muffler might have baffles broken .

No....the rpms differ from engine to engine and from manufacturer to manufacturer. RPM's are always higher at higher speeds.

My first reponse would be to remove ***********-in-law from the rear seat. LOL

Try applying the brakes lightly, does the squealing stop? If so it could simply be worn brake pads on that side however, this will usually happen a slow speeds as well. Another possibility could be your CV joint. Crawl under the vehicle on that side and check for a torn CV boot (rubber boot around the axel shaft where it comes out of the transmission/ or rear end and attaches to the spindle (wheel).

THrottle position sensor check that.

Find a quiet empty stretch of road. Go 50 mph, put the trans in NEUTRAL and shut the engine. If noise is still there, swing car left and right to detect noise differences. Could be hub or axle bearings. Not engine or trans if noise is still there. Hope this helps