Buzzing noise coming from metal conduit when circuit under load
This gets a little tricky. First NEC Table 310.15 (B) (3) (a) says 4-6 conductors in a conduit need to be adjusted to 80% of their normal current carrying capacity. So 30*.8 = 24A which is the continuous load of your charger. In NEC speak the definition of continuous is a load lasting over 2 hours. If that is true then you have to add 25% load to your charge for conductor sizing. If all of what I just stated is true, then your #10 conductors are under sized and this might be why your conductors are buzzing.

Buzzing is caused by the conductors emf (electromotive force) opposing each conductor and causing it to vibrate at 60 hertz per second. This causes two things to happen first they generate heat, which we know heat + electricity = bad, and second your conductors are moving causing splices and connection points to loosen up (also not good). Start up buzzing is common in industrial sites and sometimes allowed, but these sites have skilled maintenance crews who are supposed to have scheduled routines to maintain these circuits. In a dwelling this is not so common.

It might be a good idea for you to invest in an infrared thermometer which are fairly inexpensive nowadays, so you can scan your entire circuit while you are charging to see if it is heating up above average room temperature. It might turn out you will need to either up grade your conductor size or downsize your charger.

Remember our main concern is to prevent a burn or shock hazard so stay safe.