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Does it sound more like it is coming from the passenger side? If so it may not be behind the dash. Look underneath your car on the passenger side about where the gap between the front and rear door is about a foot or two in where the exhaust pipe runs. There is a flimsy heat shield attached to plastic with rivets. The rivets can get ripped out of the plastic and that heat shield will rattle around. That can sound like it is coming from the glove box area behind the dash

For regular oil changes and maintenance all Toyota dealerships should take you in and they use the same filters and oil. Any warranty work will likely need to go to a Lexus dealer though.