Sounds like the heads or catalytic converter

Doesn't initially tick only after I've been on the freeway for a couple minutes then will last for about 10 and then go away seems to be tge driver side? Its a Chevrolet Tahoe 2007 Lt Flex fuel 5.3l

2wd . After market headers, airintake, dual catback exhaust and recently replaced one of the catalytic converters passenger side.