popping

When I try to record something in Sonar Producer, from a MIDI to an audio track, I get a lot of popping in the background. I should say that I DON"T hear the popping while I am monitoring the recording process. However, when I then solo what I've just recorded, while muting the MIDI track, I hear constant popping all the way thru. I should also add that another new thing I am experiencing is that it's difficult to get high enough levels while I"m recording--that is,  for the bar to come close to the top of the meter. I   add this because maybe it indicates something wrong with the signal path. Of course, I turn up the levels on my Mackie 14 channel mixer to almost as high as it will go, short of getting a lot of noise. Lastly, even when I don't worry about getting such high levels, and just have the meter levels at about 75% of their max, I still get the popping, though probably a little less prominent. The popping is pretty much all thru the recording, every second or two--just like popping corn.
I have adjusted my latency readings in the recent past, so perhaps this might be a clue. If anyone has any idea why this is occurring, I'd appreciate some input. 
I"m using an older Delta series sound card, (I believe it's a "66") as well as a MIDIMAN sport 4x4 interface. This has occurred when using my MIDI data to play from various sound sources, such as from a Motif and then a ROland. Thus, it's obviously not the problem of the synth that is creating my sound.  
Thanks.
LNovik

It's probably not an audio problem, but rather a digital problem. There are a number of possible explanations, but the most likely is that the pops are caused by interruptions in the data stream because the computer can't fill the output buffers fast enough. You don't hear it while monitoring because you're probably using so-called "zero-latency" monitoring, wherein the sound is not routed through the computer but rather directly from the interface's input to its speaker or headphone outputs. If this is indeed the source of the pops, it can usually be easily eliminated by increasing your buffer sizes.

Thanks Cactus music, but using the same system in the past few years, I have been able to record without these pops. As for bitflipper's suggestions, I would greatly appreciate some quick suggested starting point of where to find the page to increase the buffer and how much to do it by. I ask this because when I now go to Option\audio, the first page is shown, and doesn't even let me edit the latency. There is this box. 2/3 of the way down that is labeled Mixing Latency. It has "Buffer and Playback queue," and "Buffer size," the latter which is that adjustable X axis. However, it isn't highlighted and I can't adjust it. Perhaps I have checked something that is making this not available. 
 
When I go to the 2nd page under Advanced, there are some choices about latency, I believe. Near the top it says "File system, Playback I/O buffer size. It is at 128 and I CAN adjust this. I guess I'll try 256. The Record I/O buffer size right next to it is at 256 and cannot be adjusted. 
There are lots of other things on these pages, and I could try to describe each setting. If anyone  knows how I can take a snapshot of each of them, I could do that also. 
Thanks again for your time.
LNovik

Boy,  bitflipper was right there helping me at first, and I was getting so excited that he might help me with my problem. Then, he deserts me! I'm starting to think he a...a....Cake teaser!
 
How about this: can anyone just tell me why I can't seem to adjust the latency or buffers on my first  page of Options/audio? As I've said, I do see the box near the bottom of that first page, but it appears in dull font--meaning I can't adjust it. I used to be able to easily do this, so I am assuming something else that is checked is making this unavailable to me.
Thanks.
 

When I had an M-Audio interface, it was not a Delta, there was a program loaded in the tray (now called the notification area) used to setup the interface.

Thanks for that input. I was easily able to find the M Audio icon right in my tray (the lower right corner of my screen.) I opened it and found that the first screen had the buffer controls. I turned up the buffers from 256 to  512.
The bad news is that this didn't seem to make any significant difference. SHould I go to  1024? SHould I just get a new audio card. Perhaps I'll look for an M Audio forum.
Thanks
LNOvik