50k is350,sounds like belt or pulley bearing but nobody else seems to have had this issue(another site listed a harmonic balancer going bad). At idle squeal comes and goes but turns constant by 800rpm and it progresses in pitch as rpm's increase.

 

Time to stop by at your local dealer ship. It covers by powertrain warranty

 

water pump or alternator pulleys are my guess.

 

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I did a google search for lexus is350 water pump noise,it led me to a you tube video titled is350 belt chirp.Mine is making the exact same noise,to bad the video producer did not say what was causing the noise.

 

Water pump failure on 2ISs is very common unfortunately. Either they leak or their bearing fails. Good thing is that the water pump is covered under the manufacturer's factory powertrain warranty.

 

Mine turned out to be a bad belt,supposedly the only time the water pump goes is when Toyota red coolant is not used.The old belt looked fine ,although for 20$ I thought I would give it a try,I got lucky ! All literature I read said it was a pulley alignment issue ? The dealership said it was either my alternator or water-pump.Applying soap to belt allowed me to tolerate the noise and do a little research.