I'll come right out and say it, I'm a noob when it comes to guitar. I played for years and never really dedicated myself to it now as a adult I never want to put my guitar down. I had a question for anyone reading who might know or anyone that would like to put thier .02¢.

I recently purchased this epi les Paul from my local GC according to the sales kid the previous owner gigged with it a couple times and traded it in for what I don't know. I love the weight and feel of a les Paul been my favorite guitar for a long time. When I picked this one up however I instantly bonded with it. The sticker inlays the tones and action were like gold or like this guitar was meant for me to own. My question is related to the strings or the D string in particular its currently got a smooth d string and being a noob guitar player I have never seen this. I own a Jackson and another cheap epiphone gt and neither of those have a unwound D string. It sounds amazing like I said but occasionally I get this twang from the D string as I play it almost like if your picking excessively harder. Can anyone shed some light for me? I appreciate all responses to my probably idiot question I was planning on putting Ernie ball regular slinky on this guitar as everyone seems to reccomend. Here are some photos thanks.

Could be a thicker G string? But they also make flat strings that are more popular with Jazz players so it could be a flat wound D-string but probably unlikely.
Just another Sheep in the design of the Almighty Machine.

Gibson 60s Les Paul Tribute (Sunburst)
1999 Ibanez RG470 (TitaniumIce-MIJ)
Jackson RR3 (Trans-Red)
Peavey 6505+
I got some Ernie Ball cobalts on the way also decided to remove the skull inlays and went with the traditional Les Paul trapeziods.
I couldn't wait for the cobalts to arrive I just strung it with Ernie Ball regulars and I see now what all the fuss is about I'm pretty happy with the feel of the regulars the tones are much better as well.
Wanted to update, the Ernie Ball cobalts are probably the best guitar strings I've ever played. If your a new player and you don't know how old your strings are or what brand they are spend five bucks and get some because there is a huge difference. Some pics for your enjoyment
The old skull inlays actually discolored the fret board you can see in this photo. Is why I opted to inlay the first fret.