Macbook Air Fan Constantly Running

MacBook Air - purchased new November 2017 (5 months old)
MacOS High Sierra 10.13.4

My Macbook has been having the following issues:

• Gray loading bar on startup. Mac startup sound plays occasionally but most of the time it doesn't.
• Fan immediately turns on and stays on except when laptop is asleep (after a minute or so), restarting, or when I open Siri.
• Overall performance is laggy, and that rainbow wheel of death has been appearing (never happened before)
• particularly slow with Chrome, cleared cache, etc, no real difference.

I tried resetting the SMC but it didn't seem to make any difference. This whole ordeal occurred about a month or so ago, then stopped, and started happening again this past week. I checked the CPU, nothing is running over 20. I have plenty of space left on my computer, I checked for malware and everything is clean. I don't play any games on this computer anymore, but one of the first times it occurred was after playing about 2 hours of the game Runescape in February. I promptly deleted it and haven't played it since.

I've browsed dozens of other forums, people seem to have fan-related issues that are caused by things that aren't relevant to me. The closest I could find was this Apple support posting: https://discussions.apple.com/thread/8254768?answerId=32947383022#32947383022

The OP seemed to have the same issues as me (I noticed that they mentioned opening Siri would stop the fan and, sure enough, after trying it the fan stopped until I closed Siri). Unfortunately, their problem was "solved" after taking their Macbook to the Apple store, where they were told the issue was a faulty logic board and charged $475. As this is a basically brand new computer, I'd rather not pay any more than I already have.

Note: as I typed this out, the fan slowly quieted down and stopped running so heavily. While I'd like to think that the problem is solved, it would be nice to know what the problem was to begin with, since it seems to come and go for no apparent reason. Plus, the gray startup bar is unexplained as well.

 

It's under warranty.
Take it back.