Bmw 1 series e88 convertible

E88 2012 118i petrol 37k manual GF12 HYO no codes no lights. 

Engine makes a growling sound when hot,,,,, not on cold start only after several miles,,, had MAF changed but still the same,,,, used PPF/GPF petrol additive in the tank to clean particulate filter which someone said bmw fitted these filters to older bmw,,,, but still the same,,,,,

Also now there is a rattle /loud ticking for 1 to 2 seconds on cold start then goes quiet,,

I only do short runs to work everyday,,, only motorways for 10 mins every other week. 

The car has been well looked after and had FSH and major service last year.

Please help as no one seems to know what they are on about and it's costing me money to try and fix. 

Thank you so much 

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