Wierd metallic "ping" after start up...'98 V70

[SonicAdventure]

About 2 weeks ago, I was pulling out of a parking lot after a short drive and I heard a strange metallic ping come from under the hood. From the drivers seat with the windows down, it sounded like a bolt sheard off or broke...

I had just put it in D and was going about 5-7 mph. Opened hood checked under car, could see no immediate evidence of anything broken. Car continued to run fine.

2 weeks later (yesterday) coming out of gym parking lot, idling as I'm about to pull out onto road, heard a slight clunk or thud as I accelerated from 0 to 10. Checked again, nothing.

Now I have probably gone 200 or so miles between incidents and performance has not changed and nothing seems wrong (no stalling, wierd handling issues, wierd motor sounds, fuel consumption is normal) but SOMETHING is not right. Why would I hear a metallic ping or thud sound like that?

About to go hook up the OBD software. CEL has been on for months due to Evap leak (I know the issue its a fuel tank breather hose I just haven't gotten around to fixing) but I need to see if anything has been added to the list.

One thing I did notice was I'm about 1 1/2 quarts low on oil.

Any ideas? I know it's a pretty random question especially since no obvious issues have shown themselves in the wake of this... Thanks

[abscate]

The ABS self test occurs at roughly this speed, but that's more like a burp or buzz. Lasts about 1/3 second and you pass advanced situational awareness if you hear it

[SonicAdventure]

Did the OBD thing this AM, everything checking normal still only the Evap code. Car runs fine, no other unusual noises, smoke, vibrating, etc.

[theWIFES_S70]

I was getting a THUMP-THUMP-THUMP right before getting a Check Engine light flash on the dash (P0455...) I have since repaired my vacuum elbows and haven't gotten that sound since. (Fingers crossed!) How are your elbows and all your EVAP hoses?