If its a rattling that goes away in about 2-6 sec its you timing chain running dry until the crankcase oil is pumped up. If it still rattles while at low idle(warm and in drive) you most likely have a bad chain tensioner or guide. MANY 95-96 maxima's had this problem-Nissan has a technical bulletin on this. If this is the case....Replace all three chains/tensioners/and guides SOON...severe damage could result to the engine and timing covers....timing chains cost $1000-1500 to replace at dealer.n (ouch!!!)