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.
SEU is special
There was once an exception in Code that allowed SEU cable (and only SEU cable, not NM or other such) for hot-hot-neutral to ranges. This was only allowed due to intense lobbying by the appliance industry, and was outlawed in 1989 when Reagan handed the reins to George Bush Sr.
Since it was once legal, this setup is grandfathered for an old 3-prong range. But only for ranges -- for nothing else since it lacks a ground.
And then Ground Retrofit rules happened, allowing you to wire just a ground from that range outlet to the nearest place with #10 or larger ground wire back to the panel - a (wired ground) water heater, air conditioner, a metal conduit that is continuous back to the panel, the grounding electrode wires from panel to ground rods, etc.
Retrofit a ground wire
Congratulations. There you sit, with a 4-wire connection. You have 2 hots (black wires), neutral, and the ground you just retrofitted. This setup is now totally Code legal. Be careful to wrap the old braided neutral with tape - it must not accidentally touch the ground wire.
Neutral is not Ground, and they must be kept separate (except for the N-G bond in the main panel).
... Now you can fit a 120V receptacle there
At this point, you can pigtail off the 3 wires - one hot, neutral and ground - to attach #12 or #14 wire for your outlet, and go re-breaker the hot-in-use to 15A.
Further, you would be able to convert this back into an electric range connection in the future, with the modern, safe 4-wire type of connection.
Pigtailing off aluminum is tricky. Wire nuts won't cut the mustard. The purple wire nuts are garbage, and the Internet is thick with pictures of melted and burned purple wire nuts. What you need is a Polaris connector (AKA AlumiConn). Turns out copper wires work just fine on aluminum lugs, and that's what these are. Two lugs back to back, wrapped in insulation. Either factory wrapped, or you-wrap-em-but-don't-mess-up.
Your wires are supposed to be 4 AWG but might be 6 AWG. Alumiconns won't cut it, they only work up to 10 AWG. So you'll need a proper Polaris connector (3 of them). Now, these all support quite a range of wire sizes, but get ones that are barely big enough for your wires. Otherwise you're dealing with needless bulk and expense. So don't just grab one that supports fat 2/0 wire, get one whose largest size is #4 (or #6 if you know your wires are that). If you can't find any that support #14, you can bump your pigtail size to #12.
Plan B: If one SEU wire is white or white-marked
If you get in there and discover one of the SEU hot wires actually is white or has 3 white stripes, then that wire is usable as a neutral wire. Then you can avoid retrofitting the ground. Re-task the braided neutral to be ground. Re-task the neutral-marked hot to be neutral. Pigtail with Polaris connectors, and you're done.
Best Answer
There is really nothing wrong with having a bigger wire. Not knowing how long your future is. Would put in a over sized conduit in emt to handle ,future wire. 1 inch emt. pull in your 12 wire. when you do change it out .Use wires to pull in new ones. Codes may change by the time you upgrade.And wires may not meet new code and be waste of money spent. Or pull your 8 wire add pigtails fine to .