YODAONE

Not advocating brand selection for serpentine belts, but why replacement occurred on what appeared to be a perfectly fine belt...

Have replaced in past 10,000 miles with OEM parts; Fan clutch bearing bracket assembly, tensioner pulley, idler pulley, alternator , power steering pump, AC clutch bearing....

However, still noticed noise on cold start up, less so at operating temperature....

The serpentine belt was Gates brand and visuslly appeared to be in good shape.

I acquired a Mitsubishi belt (with Toyota P.N. on spine ) from Lexus..about $50.with tax.

After installation, noise reduction.

Possibly the Gates belt,,at least 4 years old, had hardened...the spine appeared slightly rutty,

It now resides in trunk as a spare.

dveneman

Mitsuboshi?

Superfast1

I used the top-of-the-line Gate serpentine belts w/ EPDM (Ethylene Propylene Diene Monomer) rubber in both of my 97 & 00 LS400 & have zero issue w/ noise even at cold start.

YODAONE

The Gates belt was at least 4 years old and installed on factory original pulley driven components so perhaps the rubber had worn umevenly and or hardened somewhat...

Superfast1

I was going to say check your belt tensioner but you've already changed it so it probably due to what you've said.

RA40

iTrader: (6)

Some belts are weird in that way. Had one on the Corolla that was like that. Was new and it squealed a bit each cold start and while at temp. Squirt a bit of water on it and it would quiet down. Applied a belt dressing-conditioner and it would last about a couple K miles before coming back. Replaced the belt with the same OEM part and all noises gone, has been good for the last 18K. Nothing else replaced.

PureDrifter

iTrader: (10)

It's likely minor size variations on the belts.

Mitsuboshi is a japanese OEM supplier for belts, serpentine and timing, in the LS400.