Hi AMV, I have both conditions.
I think my IBS might have been a stress response combined with poor nutrition and overdoses of coffee, and as I didn't know what was causing my pretty severe bowel symptoms for a long time (NHS, takes forever) that might have added to my stress levels and ultimately also helped trigger tinnitus. Both can be stress related, so definitely try to reduce that.
I rigorously cleaned up my diet and have also found I don't deal with gluten well. Now my IBS is very much under control and I am even at the point where I am thinking that my IBS diagnosis is simply my doctor not knowing what else to call it. I don't know if I really have a bowel condition with a name, or that after 30 years of industrialised food (processed, packaged, additives, colorants, artificial sweeteners, etc.) my bowels decided to make a stand. Poor or lacking nutrition can detrimentally affect your vitamin levels and intestinal flora.
I don't know if you can find an orthomolecular dietist near you, but I suggest you find one and see what they can tell you about your diet. It will be an eye opener. They test your blood values and can do a stool test and so determine if you have vitamin deficiencies or off-balance intestinal flora and so give you an idea of what to change in your diet habits. In my case they also supplied a food plan, not to diet and lose weight, but to get those nutrients back in that I was lacking and need most for a healthy bowel.
Cheers