Welds on the catalytic converter heat shield can corrode causing a rattle during acceleration and possibly causing Check Engine Light illumination. The common repair for this issue is replacement of the damaged catalytic converter.Google+
Car Problem Reports
Nissan Altima Rattle/CEL Due to Cracked Welds on Catalytic Converter Heat Shield
Nissan Altima Problem
Exhaust & Emissions Affected: 3.5L V6
Average Mileage: 72,416 mi (30,000 mi - 178,000 mi)
Visitor, 2007 Nissan Altima, 40,100 mi
The heat shield welds came loose on catalytic converter which was causing a loud noise. Had it fixed for under $100.
Visitor, 2009 Nissan Altima, 120,000 mi
The car would have a rattle sound once i started it and when driving at slow sppeds, especailly when first driving off.
rattle noise coming from the engine during acceleration.
Visitor, 2012 Nissan Altima, 47,654 mi
Same problem, welds on the heat shield for catalytic converter came off causing rattle from 1500 rpm - 1700rpm and low idle. Had local shop weld back on. Fixed problem.
Multiple misfires cam a n b altima knock sensor diagnosis
Visitor, 2008 Nissan Altima, 63,000 mi
Had to replace the entire catalytic converter for $800 including parts and labor.
Visitor, 2007 Nissan Altima, 66,000 mi
Have a rattle upon first starting my Altima. Goes away after it warms up a bit. Haven't fixed it yet but looking for a solution
Visitor, 2007 Nissan Altima, 36,000 mi
Visitor, 2006 Nissan Altima, 57,000 mi
Rattling noise at low speeds, usually early in the morning. Diagnosed as a heat shield problem and fixed for pretty cheap.
Visitor, 2008 Nissan Altima, 30,000 mi
Rattle occurs on engine start. Typically occurs on a cold engine.