Elantra grinding on motion

We need to know if the noise is from the trans or the engine - the way I tell is I will start the car in park and listen to see if the sound is present when the trans is not engaged - if it's not engaged and it's grinding, it is potentially a faulty engine (this is very common with pre-2020 Hyundai/Kia models, they all had some issue with the engine until 2020 when they stopped trying to make the Theta II work and went to the Smartstream) unless it sounds like a timing belt squeaking or something like the AC compressor is going bad. This does introduce some minor risk of damaging it further, but rev the engine to 2-3k in park and see if it starts to make the sound as well if it is idling to rule the trans out. This does not mean it has a bad trans, but it does indicate the trans might be bad.

Normally I'd consider this test a last resort but given Hyundai/Kia has had issues making an engine that doesn't have catastrophic issues for 15+ years, you need to rule this out first. Sometimes it's a pulley especially if it's squeaking, but way more often then not it's internal damage. These use the Beta II engine, which like the Gamma engines have fewer problems but they are still kind of prone to Hyundai oil consumption issues. If it is burning oil and you rev test it with low oil, hat will kill the engine if it burns 1-2 quarts and you do not check first. You absolutely need to check the oil first before you rev check it.

The Smartstream is holding up a lot better then the Theta II and others, but they're still being treated as cautionary until they regularly reach 150k miles and it's clear they hold up.

If you have long hair, you absolutely need to use a hair tie for this! You are in the engine bay if you need to see where it's coming from!

If you find the engine is not doing it in Park with the trans disengaged, drive the car with the windows opened up and listen to the wheel bearings - you want to vary the speeds a lot, so do this in a neighborhood OR parking lot. Especially as these age out, the wheel bearings are not a disposable part but once you hit ~130-150k miles, it's not unheard of for them to start to go bad like this. You will need to order the one that's affected on it's own as there is no way to interchange a left front for a left right, as they are unique to each side - even the rears. Without knowing which one is bad search this: 2000-2006 Elantra [bad bearing] wheel bearing - listen for growling or howling. Check the brakes too to be sure since brake pads "squeak" when they are nearing end of life.

If the wheel bearings sound fine, it is also commonly the CV Joint on old Hyundais as well - listen for clicking/grinding. Same search to find this part number. Each one has a unique part number: https://www.hyundaipartsdeal.com/oem-200... and the SM can be found here: https://www.allcarmanuals.com/factory-se...