2 quarts low might cause the oil pressure light to come on at a stop sign or idling at low rpm, but if you got a significant engine knocking sound and a steady oil pressure light while driving on the road, most likely you were more than 2 quarts down. There’s no benefit to the shop techs to tell you that of course.
No matter where you have oil changes performed mistakes are possible. The tech may get a phone call in mid-stream and forget what they were doing when they return, etc. So good idea to check the dipstick yourself before leaving the shop, and that there are no obvious leaks under the car; then again when you get to your next destination, and once more the next morning. I know it seems like if you pay to have the job done by a professional shop or business who offers the service you shouldn’t have to check their work. But alas, you do.
I think the business owner would appreciate to know their techs are not checking the customer’s dipstick before turning over the keys.
The problem with the oil pressure light is that it usually only takes about 4 PSI to shut that light off. That’s not enough pressure when it’s in a boxing match with 1800 PSI in the cylinders.
I no longer let anyone else do my oil changes, but when I did, I pulled out of the bay but not off the property any check for leaks under the car (I kneel on a floor mat and then I shut it off and check the dipstick. It will usually 1/4 quart low because some oil has not drained back yet.
I have found overfilled crankcase ( the attendant assured me it was ok because they didn’t charge me for the extra quarts! He was astonished when I made him drain the extra out. ) I have also found a loose oil filter dripping , a loose drain plug dripping , An air filter assembly completely taken apart and not reinstalled when I would not let them replace a perfectly good filter. What I didn’t find until later was a broken cabin filter cover when I would not let them replace a cabin filter I had changed only days earlier It was $10 rather than the $60 they wanted. I also found two mangled drain plugs, apparently some guys at oil change
places only own vise grips.
The place that left the air cleaner assembly apart appoligizer and gave me a coupon for my next oil change free. They were also one of the places that mangled the drain plug. I never used the coupon.
There’s an often run radio commercial for one of those chain shops who’s name rhymes with “iffy cube” that states you can rely on the “highly trained technicians at iffy cube”. They may be highly trained at something, but it isn’t auto maintenance.
In defense of the fast lube facilities I will say this. Not all should be painted with the same incompetence brush.
There are several in my area who have been in operation for decades and have good reputations.
Some good friends of mine in Tulsa who own multiple cars have been having their cars serviced at a nearby fast lube facility for almost 20 years with never a problem.
The fast lubes predominantly do oil changes but if you look at the percentage of botched ones compared to the number of problem free oil changes the percentage may be relatively small. JMHO anyway…