I moved your thread here to the notebook area so if another owner has experienced a similar audio issue they can reply.
I don't own your machine but when you get it back you might try removing the ASUS software and updating the driver. Maybe even look for a newer driver directly from realtek or whoever makes the audio chip. It could just be some enhancement software bugging out rather than a hardware issue. The fact that it delays a few seconds after startup might mean some software is loading and messing things up.
Regarding the RMA, that's fairly typical for laptops. Most laptop warranties say the manufacturer will repair or replace at their discretion and it usually takes several failed repairs before they throw in the towel and replace it. It sounds like the parts were out of stock so they were considering a replacement but ended up finding the part and returned to the repair option. There's not much you can do though since ASUS is doing what your warranty terms say it will do. If you really want to be prepared you can research whether there are any lemon laws in your region. A lemon law requires the manufacturer to replace a product that is excessively faulty. However if you've had a single repair that's not excessive yet.
If you aren't getting sufficient communication from your local facility you can post in the Service Inquiries section of this forum. Someone from ASUS can follow up and get more information. Just make sure to read the sticky rules thread before posting in that section.
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