Idle bobbing (not the regular idle dip)

EDIT: Turned out to be a bad coilpack


Ok, so I've posted this on S2ki and have yet been given any possibilities, but here is my post:

I just did an oil change and switched from Castrol 0W-40 to Shell 5W40.
I did everything correctly.
I did not drain the transmission before anyone asks.
I let it drain for about 10-15 minutes before replacing the drain bolt, filter, and filling it with the new oil.

I filled it up, it took pretty much exactly 5L of the engine oil and I ran it a couple of times and made sure it was just under High on the dip stick.

Took it for a drive around one block and noticed when I go from a stop in first gear, it feels really rough and bumpy between 2-3k rpm or so...
after that is fine, but I didn't want to rev it too high as it worried me..
It's hard to explain, but it pretty much felt like I was driving a boxer (if I were deaf, due to the vibration) during that rev range.

Anyone ever experienced this?
I'm not sure what to do..
I don't want to empty $50 worth of oil, fill it back up with $80 Castrol to find the problem isn't gone..

CEL isn't on.
Checked if I bumped anything during the oil change. Everything is still connected.
When I warmed it up after checking the oil the last time, I blipped the throttle and it made a pop sound, then noticed it spat some black crap on a cardboard box behind my car's exhaust tips..

Any help is appreciated.. Thanks

So when it idles, it makes this sound (listen close. it's like it 'bumps?' the revs down). Any ideas?
http://www.youtube.com/watch?v=wxpXAyh0Vww