2016 Prius C -- trouble starting, check engine light, weird sound

Hello there! Did a quick search and didn't see my issue, so I'm posting. I don't know much (anything) about cars and don't want to get ripped off by an unscrupulous mechanic.

I have a low mileage 2016 Prius C 2 (~17,000). I didn't drive it for an entire month around May. When I finally got in the car, the battery was dead. AAA came to jump it, but ever since then it's been having trouble starting, which got worse this past week. For the past 2-3 months, when I turn the key in the ignition, all the dashboard lights come on and won't turn off. Then I turn it off, wait 30 seconds, and when I turn it on, it starts normally. Sometimes it takes 3 tries instead of 2.

Last Sunday, I drove it a short distance to run an errand. It had a lot more trouble at first--took about 5 tries to turn on. Then, when I went to go back home, it took about 20 minutes to get it started. When I turned the key, just the check engine light went on and nothing else. This happened several times. Then, all the dashboard lights went on, but they were dim and flickering. Finally it turned on normally. I drove it 2 other times earlier this week and it took 3 tries to start but then drove normally.

Yesterday I got in the car and just got the check engine light the first time. Turned it off, turned it back on, and all the dashboard lights came on. Then it started making a weird sound--like a low screech/drone from the engine (kind of like an out-of-tune violin). I turned the car off and the sound continued! I turned it on again and the sound stopped, but I didn't want to take the risk of driving it.

Any idea what this could be? And does anyone have recommendations for a good mechanic in Los Angeles (East side)? My normal guy is not answering his phone.