grand scenic 1.6 power loss

Hi all hope someone can help I have 2007 grand scenic 1.6 petrol I have a general power loss difficult to go up hills and top speed around 80mph the engine squeals when starting I am getting around 26mpg have changed air filters and spark plugs.(no engine ware shown on plugs) There is no warning light on dash and replaced brake pads due to slight squeal but no binding



Also when comeing off gas slight sucking can be heard along with ticking when running was thinking misfire but no lights anyone any ideas