Take my advice and return it under Warranty - don't attempt to do anything with it as it is not your problem.

With sound "off", you shouldn't get any noise, apart from normal fan sound, so may well be a fault (assuming you don't make a habit of throwing coffee, or something, over laptops).

If you are saying that you have had the SAME problem with a previous laptop, from same source, there may be a "batch issue". I would suggest contacting the manufacturer, with laptop serial number, to ask if they are aware of a problem. They may well be aware of an issue, and have a remedy. I would stress, DO NOT DO anything, yourself. Refer any suggested remedy back to your supplier. It's their responsibility to sort it, not yours. If YOU attempt any "repair", even one suggested, by the manufacturer, you could invalidate warranty.

Another couple of things to consider.

Are the speakers right next to the laptop, and not a distance away?.

Are the connecting cables or connecting power supply okay?.

At the end of the day, you've probably got little choice but to return it to your supplier, again. If it makes the noise, fairly frequently, it shouldn't be a problem for them to check it. Given the history, you may be entitled to a refund, on the basis that you have "lost confidence in the product", but if FE spots this post, he is much more familiar than I with consumer rights legislation, and may advise further.