95 sentra question -engine noise

i was test driving this model for a friend, and it sounds like it has a valvetrain roaring noise. the noise is at idle and goes away while accelerating and at speed while driving, but is pretty bad at idle. the valves aren't ticking and oil level is good, its justa strange noise that i couldn't easily identify. it is not coming from any of the accessory drives (ac, alternator, etc) does anyone have any experiences they would like to share? the engine is the 1.6 liter i believe- and this is an automatic trans. the odo is 101k miles, which is why i am really bothered by the engine noise. my 91 sentra with the same engine sounds like silk with 144k miles. thanks for any suggestions! btw- my theory is timing chain guides worn out and gone, and the noise is the chain hitting the timing cover- could get nasty pretty quick! anyone else have any hints?