@2haist...
I read through this thread and something I did notice .. according to your "screen snip" in your last post is that you are using a "generic audio driver" .. in MY experience that CAN cause issues... it's GENERALLY best to go to the manufactures of the "chip" rather than the computer(in this case Dell) itself to get the most updated drivers .. it CAN be a pain in the backside .. but MANY TIMES worth it in the end
I would advise .. going to the Dell site OR Realtek site and download the SPECIFIC driver for you sound chip...
If you use the Dell site .. it SHOULD be included in... I believe chipset drivers SPECIFICALLY for your model/style of laptop .. which if I'm not mistaken Dell site SHOULD be able to auto-identify via the embedded service tag when you go there...
Dell support site
OR
If you use the Realtek site .. you would have to know what chip is being used for sound do a search for the specific chip ... and download the drivers and install them.
In order to identify the SOUND CHIP .. you can use quite a few different programs to find that out ... I PERSONALLY recommend ..
Speccy or any other recommended software that looks deeper into your than Windows device manager(in my opinion) ...
Just remember whichever way you go you want to MOST RECENT(newest) driver available for your sound chip OR chipset.
Best of luck,
LoneWolf
P.S. IN MY OPINION... any shop worth their reputation WILL/SHOULD tell you EXACTLY what they did to your machine.. and explain to you as best they can so you can understand what they did.
***edited to add Dell support site direct link ***