tlewis - agreed yours sounds exactly like coilpack.
Please don't use aftermarket replacement packs, no matter how cheap they are or how many decades warranty they claim to offer! Oh, and always keep at least one spare in the boot, if a coilpack packs up completely it makes the car almost undriveable and you're pretty much stranded. Also be aware you need a 10mm spanner and 5mm allen key to get number 4 pack out, there's a vacuum vessel and bracket that have to be removed to access #4 coil.
Please don't use aftermarket replacement packs, no matter how cheap they are or how many decades warranty they claim to offer! Oh, and always keep at least one spare in the boot, if a coilpack packs up completely it makes the car almost undriveable and you're pretty much stranded. Also be aware you need a 10mm spanner and 5mm allen key to get number 4 pack out, there's a vacuum vessel and bracket that have to be removed to access #4 coil.