Imperial stout still outgassing or infected?

So here's the skinny...

I brewed a dry stout and planned on using the yeast cake to ferment my gigantic imperial. Unfortunately, I was unable to find time to brew the imperial stout until about 5.5 weeks after the dry stout finished. When I brewed the imperialt I racked right onto the yeast/trub from the dry stout (fermented with WLP001). Fermentation moved along and everything seemed fine/tasted great. After primary was done (about 10.5% abv) I racked to a secondary and added some oak and chilled to 55 for what was supposed to be a couple of months. Looking at the beer now it is somehow still making the airlock bubble after 2 weeks in the secondary and about 3.5 after I brewed it. I pulled a sample and tasted it and I think I may detect a slightly sour flavor developing. It's hard to tell due to the high alcohol content and the beginnings of some oak flavoring. Is it possible this beer is still outgassing or does this sound more like an infection? I'd hate to use the fridge space for the next few months if the beer is just going to end up being infected...

Thanks for any and all feedback!

You brewed a huge beer and it tastes funny after 3.5 weeks. Sure it does.....

Gassing from the airlock is no big deal.

Keep with your schedule.

David