AS I said
I hope you will hear good audio without - the rice crispies
and you now reply
So, this worked!!! I currently have my headphones plugged into my Dell monitor. Sound is coming through my displayport. I hear no crackling/popping!!!
I am overwhelmed with excitement!
I am pleased it worked, well done to you on sorting out that setup, from my guidance.
I cannot really give you a definite reason. I doubt if anyone can.
The possibilities
1. A bad connection on the ports of the headphone and speaker -out on the computer tower.
This does sometime occur, especially if there is frequent connection and disconnection.
The minijack socket becomes worn, however this usually becomes evident in gradually increasing stages.
2. A fault - most unusual but it can occur on the sound chip on the motherboard. The realtek is integrated audio, I mean there is no actual sound card. This in your case is not the apparent problem, as you say the pops and crackles also occurred with the Sounblaster card.
3. Is the computer power connected directly to the AC supply or through a power surge strip. If the latter ios the monitor also on the power surge connection. Sometimes a less than perfect earth can cause such interference.
There is a lot of possible EMI and RFI in computers
Electro magnetic Interference and Radio Frequency Interference.
RFI/EMI in my earphones?
4. IT MAY just be, that something such as the aforementioned faulty earth was effecting the headphone and speaker cables when connected to the computer but not on the monitor.
The DP cable from the card to the monitor is as you will realise less likely to easily pick up interference, than the relatively poor shielded headphone and speaker cables and connections are.
5. The audio of course is now coming from your Nvidia card and not the Realtek.
6. So the answer is, although I have some degree of knowledge about it, having in times gone by, been involved in transmitting radio signals across the world and indeed bouncing them off the moon, I cannot tell you the cause, without being there at your setup.
7. I suggest you do the following
A. Check the inside of your computer tower. Make saure if you have possibly disturbed a power connection that it is fully made. AND whilst inside check for dust build up on fans and the CPU fins and fans
B. If it is connected via power surge and you wish to pursue the testing, try a direct connection without the power surge bar
C. As on the link at 3 you can buy clip on or rings to which you wind the speaker cable say on four turns, known as ferrite chokes - meant for RFI and to a lesser extent
although not designed for them, reasonably effective on other sources of interference.
D. If you had a wireless internet adapter or a wireless keyboard etc, I may have suspected that
OF COURSE on the inside the tower, ensure disconnected from power.
Do NOT touch any chips on ram etc AND before even touching any circuitry, ground any static in your body, by touching firmly the metal case inside on bare metal of the computer tower.
You may think this a little OTT, but I have know people work on a carpeted area, not follow that advice, grabbing hold of a ram stick by the chips on it, instead of the edges of the stick and in the right conditions, it is goodbye that ram stick. NOT OFTEN but certainly can happen
5. I would, if you do not find anything from the above and before even thinking of ferrite chokes, try connecting the computer to a different power source in your house.
For example if you know a little about electricity circuits, then usually the downstairs is one ring, the upstairs is another and the cooker if electric or the hob, are normally separate circuits. IT MAYBE that the circuit your computer is on, has an earth fault somewhere and of course the earth is common throughout the circuit.
IF there is a fault you may find that it exists on all outlets on that circuit, but not on another ring or separate feed to cooker etc. This slight fault may now be hidden as I said by the use of the DP cable for the sound and the headphones off the monitor. Other equipment in use, may not of course be sensitive to such.
6. FINALLY it has been my pleasure to help you, you are great to work with. Please do let me know how it goes.
Regards
Stay safe in the crisis