Rattling from Engine

Check your owners manual because maybe your vehicle is designed to run on premium gas, If you run a lower octane the engine will ping or rattle when its under load (getting on the freeway or going uphill) here are the MDX engine specs: 2004 Acura MDX Base Sport Utility Performance & Efficiency Standard Features - 3,474 cc 3.5 liters V 6 front engine with 89 mm bore, 93 mm stroke, 10 compression ratio, overhead cam, variable valve timing/camshaft and four valves per cylinder - Premium unleaded fuel 91 - Fuel economy EPA highway (mpg): 23 and EPA city (mpg): 17 - Multi-point injection fuel system - 19.2 gallon main premium unleaded fuel tank - Power: 198 kW , 265 HP SAE @ 5,800 rpm; 253 ft lb , 343 Nm @ 3,500 rpm